zfsd(8): Close a race condition when onlining a disk paritition

When inserting a partitioned disk, devfs and geom will announce the whole
disk before they announce the partition. If the partition containing ZFS
extends to one of the disk's extents, then zfsd will see a ZFS label on the
whole disk and attempt to online it. ZFS is smart enough to activate the
partition instead of the whole disk, but only if GEOM has already created
the partition's provider.

cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h
cddl/contrib/opensolaris/lib/libzfs/common/libzfs_import.c
	Add a zpool_read_all_labels method. It's similar to
	zpool_read_label, but it will return the number of labels found.

cddl/usr.sbin/zfsd/zfsd_event.cc
	When processing a DevFS CREATE event, only online a VDEV if we can
	read all four ZFS labels.

Reviewed by:	mav
MFC after:	3 weeks
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D11920

cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h

@@ -772,6 +772,7 @@ extern int zpool_in_use(libzfs_handle_t *, int, pool_state_t *, char **,
  * Label manipulation.
  */
 extern int zpool_read_label(int, nvlist_t **);
+extern int zpool_read_all_labels(int, nvlist_t **);
 extern int zpool_clear_label(int);
 
 /* is this zvol valid for use as a dump device? */

cddl/contrib/opensolaris/lib/libzfs/common/libzfs_import.c

@@ -914,6 +914,65 @@ zpool_read_label(int fd, nvlist_t **config)
 	return (0);
 }
 
+/*
+ * Given a file descriptor, read the label information and return an nvlist
+ * describing the configuration, if there is one.
+ * returns the number of valid labels found
+ */
+int
+zpool_read_all_labels(int fd, nvlist_t **config)
+{
+	struct stat64 statbuf;
+	int l;
+	vdev_label_t *label;
+	uint64_t state, txg, size;
+	int nlabels = 0;
+
+	*config = NULL;
+
+	if (fstat64(fd, &statbuf) == -1)
+		return (0);
+	size = P2ALIGN_TYPED(statbuf.st_size, sizeof (vdev_label_t), uint64_t);
+
+	if ((label = malloc(sizeof (vdev_label_t))) == NULL)
+		return (0);
+
+	for (l = 0; l < VDEV_LABELS; l++) {
+		nvlist_t *temp = NULL;
+
+		/* TODO: use aio_read so we can read al 4 labels in parallel */
+		if (pread64(fd, label, sizeof (vdev_label_t),
+		    label_offset(size, l)) != sizeof (vdev_label_t))
+			continue;
+
+		if (nvlist_unpack(label->vl_vdev_phys.vp_nvlist,
+		    sizeof (label->vl_vdev_phys.vp_nvlist), &temp, 0) != 0)
+			continue;
+
+		if (nvlist_lookup_uint64(temp, ZPOOL_CONFIG_POOL_STATE,
+		    &state) != 0 || state > POOL_STATE_L2CACHE) {
+			nvlist_free(temp);
+			temp = NULL;
+			continue;
+		}
+
+		if (state != POOL_STATE_SPARE && state != POOL_STATE_L2CACHE &&
+		    (nvlist_lookup_uint64(temp, ZPOOL_CONFIG_POOL_TXG,
+		    &txg) != 0 || txg == 0)) {
+			nvlist_free(temp);
+			temp = NULL;
+			continue;
+		}
+		if (temp)
+			*config = temp;
+
+		nlabels++;
+	}
+
+	free(label);
+	return (nlabels);
+}
+
 typedef struct rdsk_node {
 	char *rn_name;
 	int rn_dfd;

cddl/usr.sbin/zfsd/zfsd_event.cc

@@ -36,6 +36,7 @@
 #include <sys/cdefs.h>
 #include <sys/time.h>
 #include <sys/fs/zfs.h>
+#include <sys/vdev_impl.h>
 
 #include <syslog.h>
 
@@ -93,6 +94,7 @@ DevfsEvent::ReadLabel(int devFd, bool &inUse, bool &degraded)
 	pool_state_t poolState;
 	char        *poolName;
 	boolean_t    b_inuse;
+	int          nlabels;
 
 	inUse    = false;
 	degraded = false;
@@ -105,8 +107,16 @@ DevfsEvent::ReadLabel(int devFd, bool &inUse, bool &degraded)
 		if (poolName != NULL)
 			free(poolName);
 
-		if (zpool_read_label(devFd, &devLabel) != 0
-		 || devLabel == NULL)
+		nlabels = zpool_read_all_labels(devFd, &devLabel);
+		/*
+		 * If we find a disk with fewer than the maximum number of
+		 * labels, it might be the whole disk of a partitioned disk
+		 * where ZFS resides on a partition.  In that case, we should do
+		 * nothing and wait for the partition to appear.  Or, the disk
+		 * might be damaged.  In that case, zfsd should do nothing and
+		 * wait for the sysadmin to decide.
+		 */
+		if (nlabels != VDEV_LABELS || devLabel == NULL)
 			return (NULL);
 
 		try {